The present invention relates to an improved dye laser system and more particularly to an improved dye laser system and method for use and operation thereof that substantially improves performance and efficiency.
Dye lasers have various present applications in industrial and medical fields. Examples of medical fields in which the dye laser has proven useful are in the fields of plastic surgery, dermatology, urology, ophthalmology, etc.
Dye lasers can be tuned continuously to any wavelength in and near the visible spectrum. With the exception of the free-electron laser, that is cost and size prohibitive, dye lasers are unique with respect to tunability. All other low cost lasers operate at a single precise wavelength or at most a very few precise wavelengths. There are relatively few of these types of visible spectrum lasers so that there are large gaps in the visible spectrum that cannot be attained with nontunable lasers. Also, dye laser technology allows the output to be either pulsed or continuous at high energy output. Therefore, these features make dye lasers preferable for many applications.
Unfortunately dye lasers have a drawback that makes them unattractive for commercial use. The dye has a very limited lifespan. It degrades with use and must be replaced. This maintenance cost and inconvenience make dye lasers unsuitable for many applications, and expensive and troublesome at best.
Commercially available dye lasers use fluorescent dyes in solution as a lasing media. These lasers consist typically of (1) a laser cavity which is an optical arrangement that allows lasing to occur; (2) a dye circulation system including pumps, valves, tubing filters, a reservoir, etc., that circulates and conditions the dye solution and delivers it to the laser cavity; (3) the dye solution itself consisting of dye dissolved in a solvent or mixture of solvents as well as other chemicals that may enhance the lasing properties of the dye; and (4) an energy source capable of exciting the dye allowing it to emit and amplify light. This energy source, or pump, may be either continuous or pulsed.
An example of a commercially available dye laser, manufactured by Candela Laser Corporation, Wayland, MA. is the flash lamp pumped, pulsed dye laser. Numerous dyes may be used that lase at different wavelengths so that the entire visable spectrum may be covered. These lasers have dye reservoirs of up to approximately 20 liters. In use, the dye solution is pumped from the reservoir through a bubble filter to the laser cavity and back to the reservoir. A second reservoir can be made available since the dye in such lasers has a very short lifespan. A typical laser dye such as Rhodamine 575 in ethylene glycol water solvent has an expected lifespan of only 1000-2000 pulses in a 20 liter reservoir using 400 mg dye at output energies of 1.5 to 3 joule with the laser system at a 350 microsecond pulse duration. Throughout this lifespan the efficiency of the dye decreases, so that if a constant output energy is required, the pump energy must be adjusted to compensate for the lost efficiency. The end of useful life is determined by the energy output required. When the desired energy output cannot be maintained at the maximum input energy setting, the dye is exhausted and must be replaced. The dye and degraded dye products are removed from the solvent by passing it through an activated charcoal filter, which is initially very efficient at removing dye from solution, but must be replaced after a few dye changes because it becomes slow in removing the dye. New dye is then added to the solvent and mixed until thoroughly dissolved. This process may take an extended period of time, so that if the laser is in heavy use, changing dye is a continuous process. At the above laser's fastest repetition rate (about 1 pulse per sec) the dye would only last 33 minutes. Thus, the laser could operate at this rate for only about one hour before the laser use would have to be stopped to wait for completion of the dye changing process.
A dye laser of the above-described type has been used in dermatology and plastic surgery to treat port-wine-stains (birthmarks) and has proven to be the treatment of choice for removal. A typical treatment session of a large post-wine-stain process consists of 300 to 400 shots and takes about 45 minutes. During the course of treatment the output energy must be constantly monitored and adjusted to compensate for dye degradation. Changing dye is an ongoing process with a technician devoted to maintenance of the laser. In spite of this, the treatment schedule is frequently disrupted by maintenance.
One manufacturer, Candela Laser Corporation, has attempted to improve this situation and has developed a pulsed dye laser for dermatology and plastic surgery with an automated dye removal/replacement system that changes the dye in a small reservoir every 100-200 pulses without seriously disrupting the treatment. The dye kit for this system costs $950.00 and is good for only 5000 pulses. The energy output is constantly monitored and adjusted by another automated system. These improvements more than double the cost of the laser. The disadvantages associated with the presently available dye lasers have resulted in substantial costs of use and operation and have limited the availability of dye lasers accordingly. Therefore, it would be a significant advance if the cost of replacing the dye and solvent in a dye laser could be reduced or eliminated.
Others have attempted to extend the useful life of the dye solution in a dye laser. In U.S. Pat. No. 4,364,015, for "Compact Reservoir System For Dye Lasers", a system is disclosed that includes a by-pass loop circuit in conjunction with a main fluid circuit. The by-pass circuit disclosed in the '015 patent diverts a portion of the dye solution from the main circuit and passes the solution through a filter located in the by-pass circuit. The filter is intended to remove solute and particulate from the solvent and return the solvent to the main circuit thus eliminating the used dye from the system. A drawback of the method of the '015 patent is the necessity for the additional by-pass circuit as well as the filters associated therewith, and the eventual loss of dye with each filter pass.
Another method intended to improve operation of a dye laser system is disclosed in Sov. J. Quantum Electron., Vol. 6, No. 9 (Sep. 1976). The method closed in the Soviet article includes passing a dye solution through a filter of anhydrous aluminum oxide of the analytic grade to remove undesired photoproducts. The article disclosed an extension of the life of the dye from 1 to up to 10 pulses without significant degradation. However, according to the method described, the dye was not salvaged for further use, thus still greatly limiting the application of this method.
Accordingly, it is an object of the present invention to provide a dye laser, and a method for use thereof, with a much extended dye solution lifetime.
It is another object of the invention to provide a dye laser system that dispenses with, or reduces the necessity for, periodic dye replacement.
It is another object of the invention to provide a much more efficient dye laser.
It is yet another object of the invention to provide a dye laser, and method for operation thereof, with a more consistent energy output.
It is still another object of the present invention to provide a method and system for modification of an existing dye lasers that can be retrofitted thereto to improve performance and efficiency.
It is yet still another object of the present invention to provide a method and system for restoring dye solution degraded during use in a dye laser system so that the dye solution can continue to be used in a dye laser.